UI edge cases are not accomodated

[maxime-rainville]

The SessionLoginField doesn't currently cater to the following edge cases:

• Member without any LoginSession
• ReadOnly view
• LoginSession for which you do not have Delete rights

Acceptance criteria

• If a site customises the can view permission on LoginSession, the Login Session field is displayed when you are allowed to view session for a given user.
• If you don't have permission to view a LoginSession, but not to delete it, no-login delete button is displayed.

@silverstripeux

[clarkepaul]

I think that for all those situations it makes sense. @maxime-rainville for these scenarios does the section appear as empty or is it completely removed?

I would imagine there would be a message saying there is no login sessions or that area would be completely missing. My preference is that the area is present with a message but that would mean potentially different messages for different cases unless we can create a generic one.

[maxime-rainville]

TLDR None of those edge cases can be reached on a vanilla install of session manager, but it could be possible if third party dev give some members permissien to manage other users' sessions.

Once #62 is merged, none of those scenarios will be possible in a vanilla install:

• "LoginSession for which you do not have Delete rights" won't be possible because you'll only be able to see your own sessions which you can delete
• "ReadOnly view" can't be reached because you'll always have the right to edit your own profile
• "Member without any LoginSession" won't be possible because you need to be logged in to view your sessions, so you at least have one session.

Things will get a little more complicated if devs decide to customise the behaviour. Assuming a scenario where you've created a role that allows you to view/manage other users session:

• If there's no session, the field will be removed from the field list, so it won't show at all. You will get this state on a new user that has never logged in.
• If you don't have permission to delete the current session, you'll still get a "delete" link, but you'll get an error when you click on it.

[brynwhyman]

Noting that I don't see this issue being a priority to resolve before the initial beta/ stable release.

When docs are created in #57 that outline the possibility of altering the behaviour to give privileged users access to other user sessions, we could make the recommendation that both CanView and CanDelete permissions should be provided, as a read-only view is not supported.

[maxime-rainville]

A quick win could just be to not display logout session when the field is read-only. That's probably a 1-2 point job and would lead to less confusion than having some convoluted explanation in the doc.